Thyroprotein for Cows

by L. A. MOORE and J. F. SYKES

THE THYROID gland affects milk production. If the gland is removed from a cow, her milk decreases 75 percent. If it is put back, in the form of dried thyroid tissue or the synthetic hormone, thyroxine, her yield returns to normal. Both substances stimulate normal cows to give more milk and fat. The difficulty has been that dried thyroid tissue is too costly to feed cows, and if the total supply of the tissue were made available for feeding cows, we would have enough for only a few animals. Lately, however, scientists have found a substitute.

German scientists in 1938 found that the addition of iodine to proteins under certain chemical conditions makes a product that acts like dried thyroid tissue. The next step was taken by E. P. Reineke and C. W. Turner of the dairy department of the University of Missouri; they ascertained that iodine could be added to skim milk or casein, the protein contained in milk, under certain conditions, with a similar result. Further work disclosed that the actual hormone, thyroxine, was produced by the process.

This material can be produced more cheaply and is even more active than dried thyroid. It does not lose potency in storage. It is known variously as iodinated casein, iodinated protein, thyrocasein, thyrolactin, thyroprotein, and by the trade name Protamone. Here we shall call it thyroprotein. Until recently it has been supplied only to experiment stations and similar research organizations for experimental purposes.

Professors Reineke and Turner tested thyroprotein on 9 cows in their herd. When they fed 50 to 100 grams (3 to 6 ounces) of thyroprotein to each animal for 3 days, they had increases of 6.09 to 22.6 percent all average of 8.59 percent) in milk production. In six of the nine trials "I which fat analyses were made, an increase in the fat percentage was obtained, which, together with an increase in milk production, produced a 13.9 percent increase in fat yield. In similar tests at the West Virginia, New Jersey, and Louisiana stations, 10 to 15 grams daily were fed. These amounts produced increases of 5 to 20 percent in milk production, 0.32 to 0.98 percent in fat percentage, and 25 to 50 percent in total fat yields. The most extensive work with thyroprotein has been carried out in England by K. L. Blaxter and his associates.

A review of the data collected thus far indicates that on the average and within narrow limits the response in milk production is proportional to the quantity of thyroprotein fed. Because of limitations in the animal itself, naturally this relationship would not hold where one feeds much larger amounts of thyroprotein than shown in the chart for an extended period. As a matter of fact, excessive amounts will lower milk production. The amount used must be carefully controlled.

The response of cows to thyroprotein feeding in terms of milk and fat production appears to vary from cow to cow. Most of these variations we cannot yet explain. Several scientists, however, have found no response if the material is fed to a fresh cow and none is noted until lactation begins to decline. Likewise, very little response is evident during the last month or two of lactation; as a matter of fact, thyroprotein may tend to cause a cow to dry up late in the milking period. For best results, therefore, the thyroprotein should be fed for only the middle 5 or 6 months of the lactation period.

Professor Blaxter and his colleagues suggest that in midlactation the proportional response goes up as lactation declines, while the greater the initial yield at the beginning of the feeding the greater the response in pounds per day. It seems likely, therefore, that good producers will generally give greater increases in milk and fat than poor cows. Whether a poor cow can be converted into a good producer merely by feeding thyroprotein is problematical, because the response obtained depends partly on her inherent ability to produce. Furthermore, increases in milk follow increases in the amount fed only within narrow limits.

Although thyroprotein can raise yields of milk and fat markedly, it also can create a condition of hyperthyroidism, with a higher heart rate, respiration rate, and body temperature, and a loss in body weight. These effects are to be expected, because the extra supply of thyroxine taken into the body steps up metabolism, or the rate at which the body of the cow utilizes food nutrients. In other words, she is using up food nutrients and the nutrients stored in her tissues somewhat faster than normal.

We do not know whether these effects will harm the cow's health and reproduction if thyroprotein is fed from lactation to lactation. In the short feeding trials carried on at the various experiment stations, no permanent bad effects have been reported. The Bureau of Dairy Industry has started a long-time trial to learn more about this.

In the short-time tests carried out thus far, it appears that the heart rate increases approximately in proportion to the amount of thyroprotein fed. Similarly, as we have said, milk production increases in proportion to the amount fed. Thus, we may conclude that if a cow responds in milk production to thyroprotein feeding, the heart rate will be increased, and, conversely, if the heart rate is not increased, there will be no increase in production. Observations at Beltsville seem to substantiate this speculation.

Further data collected at Beltsville indicate that the heart rate of cows given thyroprotein is related to the level of feed intake. When the level of thyroprotein feeding is kept constant, the heart rate can be 4ccelerated markedly by increasing the total feed intake 25 to 50 percent. If the high amount of feed is reduced, the heart rate then decreases. Also, after cows have been receiving thyroprotein for 4 to 8 'Weeks and there has been a considerable loss in body weight, and milk production has declined sharply, the heart rate will also decline. It would appear that the heart rate is governed by the amount of energy the body has available for use, whether from the body tissues or from feed, or both. These observations are preliminary; we are gathering further information on them.

A disturbing factor connected with the increased metabolism is the loss of body weight of cows fed grain at the usual level. Men at various experiment stations report definite losses of body weight where thyroprotein was used; such a loss may be particularly severe in hot climates and in summer.